American intelligence agencies also warned Pakistan after the HSBC Bank blast in Istanbul last month that foreign terrorists would try to enter Pakistan to carry out attacks, the sources, who did not want to be identified, said on Sunday.
The sources confirmed a report in the Pakistani newspaper The News that said C4 plastic explosive was used to blow up a bridge in Rawalpindi, near Islamabad, just after Musharraf's motorcade had passed last Sunday.
Police say the Bali bombings last year, in which 202 people were killed, was the work of an al-Qaida-linked southeast Asian network. Investigators said C4 plastic explosive was used in one of the bombings which ripped through a nightspot.
Musharraf told Reuters in an interview last week after the assassination attempt that al-Qaida and their local collaborators were at the front of the queue of those who wished to kill him.
The News quoted one of its sources as saying that the attack on Musharraf was the first in which C4 explosives had been used in an attack in Pakistan.
"We just know that C4 is now in the possession of terrorists in the country, but in what quantity is the subject of a nationwide probe," an official told the paper.
The intelligence officials who spoke to Reuters said US intelligence had warned Pakistan after the Istanbul bombing that 14 suspects from Egypt, Sudan, Syria, Saudi Arabia, Morocco and Kenya would try to enter Pakistan to carry out attacks.
Musharraf said al-Qaida was top
of list of those wanting to kill him
The sources said a few had already entered the country and Pakistani intelligence agencies were trying to track them down.
The News quoted sources as saying that security agencies were also "intensely following" an intelligence tip that local operatives of a radical pro al-Qaida Sunni Muslim group went underground in Rawalpindi just before the assassination bid.
The paper said initial investigations had strengthened the view that US-supplied jammers installed in Musharraf's armoured Mercedes had delayed electronic signals used to detonate the explosives.
The paper said five separate lots of explosives in interconnected pouches, each weighing 10 kg, had been attached to horizontal bars on the bridge.